For an easy quick way visit http://mtgoxlive.com/orders and hover your mouse over the price you wish to move to and it will tell you how many bitcoins/$'s are required to do so (assuming you are buying/selling on mtgox exchange)As for your question on causing a rally I cannot answer that.

$1,000,000 is much larger then the entire order book on both the bid and asks sides at all public exchanges. Manipulating the market is certainly possible. However, this is a very risky activity and more likely then not you would not be able to profit from this.